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Mikuni Bs26 Carburetor Manual Verified

The Mikuni BS26 is a 26mm constant velocity carburetor, common on small-displacement motorcycles and ATVs, featuring a 24mm float height and a pilot screw setting of 1.5 to 1.75 turns out. Proper maintenance requires cleaning the pilot jet to prevent idle issues, inspecting the diaphragm for tears, and setting the float height precisely to avoid overflow. For comprehensive documentation and diagrams, refer to scribd.com

1. Construction and Nomenclature

The BS26 designation indicates:

Step 1: The Diaphragm Test (No tools required)

Before removing the top cap, lift the slide with your finger. It should move smoothly and drop with a soft thump. If it drops slowly, your diaphragm is holed or the cap is misaligned. Verified: There is a small alignment nub on the BS26 diaphragm. If you do not seat this nub perfectly in the carb body's groove, the slide will vacuum lock. mikuni bs26 carburetor manual verified

5. Common Failures and Diagnostic Codes (Verified from Field Data)

| Symptom | Probable cause | Manual verification step | |---------|----------------|---------------------------| | Hesitation at 5000 rpm | Torn diaphragm | Visual inspection; blow lightly into vacuum port—slide must rise smoothly | | Hard start cold | Clogged starter circuit | Remove starter plunger; check tiny fuel passages with carb cleaner | | Rich idle (black plugs) | Pilot screw too far in | Reset to 2.5 turns out; replace pilot jet if >3.5 turns required | | Surge at steady throttle | Incorrect float height | Remeasure at 30° angle; adjust tang gently | | High idle (1800+ rpm) | Vacuum leak or stuck slide | Spray propane around intake boots; check slide for free movement | The Mikuni BS26 is a 26mm constant velocity

Check the Needle Valve: Ensure the rubber tip of the float needle is supple and hasn't developed a "ring" or groove, which causes overflowing. 4. Tuning & Adjustments (The Verified Way) The Pilot Screw (Idle Mixture) Order (from body out): Spring > Washer > O-ring